- 5. In a DNS black list, when the facility for restricting the matching IP
- values is used, the text from the TXT record that is set in $dnslist_text
- may not reflect the true reason for rejection. This happens when lists are
- merged and the IP address in the A record is used to distinguish them;
- unfortunately there is only one TXT record. One way round this is not to
- use merged lists, but that can be inefficient because it requires multiple
- DNS lookups where one would do in the vast majority of cases when the host
- of interest is not on any of the lists.
-
- A less inefficient way of solving this problem has now been implemented. If
- two domain names, comma-separated, are given, the second is used first to
- do an initial check, making use of any IP value restrictions that are set.
- If there is a match, the first domain is used, without any IP value
- restrictions, to get the TXT record. As a byproduct of this, there is also
- a check that the IP being tested is indeed on the first list. The first
- domain is the one that is put in $dnslist_domain. For example:
-
- reject message = rejected because $sender_ip_address is blacklisted \
- at $dnslist_domain\n$dnslist_text
- dnslists = sbl.spamhaus.org,sbl-xbl.spamhaus.org=127.0.0.2 : \
- dul.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.10
-
- For the first blacklist item, this starts by doing a lookup in
- sbl-xbl.spamhaus.org and testing for a 127.0.0.2 return. If there is a
- match, it then looks in sbl.spamhaus.org, without checking the return
- value, and as long as something is found, it looks for the corresponding
- TXT record. If there is no match in sbl-xbl.spamhaus.org, nothing more is
- done. The second blacklist item is processed similarly.
-
- If you are interested in more than one merged list, the same list must be
- given several times, but because the results of the DNS lookups are cached,
- the DNS calls themselves are not repeated. For example:
-
- reject dnslists = http.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.2 : \
- socks.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.3 : \
- misc.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.4 : \
- dul.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.10
-
- In this case there is a lookup in dnsbl.sorbs.net, and if none of the IP
- values matches (or if no record is found), this is the only lookup that is
- done. Only if there is a match is one of the more specific lists consulted.
-
- 6. All authenticators now have a server_condition option. Previously, only
- plaintext had this, and this has not changed: it must be set to the
- authenticator as a server. For the others, if server_condition is set, it
- is expanded if authentication is successful, and treated exactly as it is
- in plaintext. This can serve as a means of adding authorization to an
- authenticator.